1. Field of the Invention
The present invention relates to an optical disk device for writing data to a optical disk on which a track descriptor block indicating how to write data has been recorded in a pregap portion of its track head portion.
2. Description of the Related Art
In the case of such a writable optical disk as a write once optical disk, data recorded after the recording of data is interrupted can be incorporated with data recorded before the interruption of the data recording in order to record the whole data in one complete track. On the other hand, there are methods of writing data to tracks: a track-at-once method and a packet-write method. The packet-write method is further divided into a fixed length method and a variable length method; in other words, there are three methods of writing data onto tracks. Notwithstanding, the same write method has to be employed in the same track. When the recording of data is interrupted once and then restarted subsequently, the method of writing data continuously has to conform to the method of writing data that has been employed before such an interruption occurs. For this reason, it is necessary to make certain of whether the write method conforms to the write method employed before that interruption whenever data is continuously written to a track where the write operation has temporarily been interrupted.
On the other hand, the method of writing data is indicated in a track descriptor block (hereinafter referred to as "TDB "), which is recorded in a pregap portion provided in the head portion of a track. When data is written continuously after the write operation is interrupted, it is necessary to make certain of whether the write method conforms to what has been indicated in the TDB by reading the latter method prior to performing the write operation. However, it takes about 500 mS to perform the operation of reading the write method recorded in the TDB. Therefore, when data is written according to instructions from the outside, there are required two kinds of time, namely, the time required to read the write method indicated in the TDB and the time required to write data actually and this results in lowering the write speed when viewed from the outside.
On the other hand, the conventional technique proposed in Japanese Patent Unexamined Publication No. Hei. 8-22689 is intended to shorten write time and prevent overwriting by finding each track mode in advance. In this conventional technique, the number of tracks N is obtained according to PMA information. Whether a track 1 has been written is then checked and the data mode of the track 1 is determined by its written condition. In other words, the data mode is determined to be MODE 1 when no data has been written to the track 1. Further, the data mode is determined to be MODE 1 or MODE 2 by its written condition when data has been written to the track 1. Subsequently, the length of the pregap portion disposed in the head portion of each track is repeatedly examined until the number of tracks reaches N. When the length of the pregap portion thus examined is two seconds or more, the data mode of the track is determined to be identical to the data mode of a preceding track. Further, when the length of the pregap portion thus examined is three seconds or more, the data mode of the track is determined to be different from the data mode of a preceding track. Consequently, the data modes of all tracks are determined on the basis of the data mode of the track 1 thus examined first and stored.
However, the following problems develop from the above conventional technique. That is, there is required time to read the length of the pregap portion in addition to time until a pickup is moved to the pregap portion in order to read the length of the pregap portion of one track. Moreover, the number of tracks may sometimes reach maximum 100. Therefore, it takes an extremely long time to completely determine the data modes of all tracks. For this reason, it also takes a long time until commands become acceptable when the optical disk has been replaced and this makes the optical disk device not easy to use.